Open Distributed Processing

Open Distributed Processing
Davide Rizzo Open Distributed Processing

Summary Why ODP? What is ODP? Reference Model for ODP Consistency of Viewpoint Specifications Open Distributed Processing

Why ODP? Open Distributed Processing Open Distributed Processing

Characteristics of Distributed Sytems
Remoteness: components of a distributed system may be spread across space Concurrency: any component of a distributed system can execute in parallel with any other components Lack of global state: the global state of a distributed system cannot be precisely determined Partial failures: any component of a distributed system may fail independently of any other components Asynchrony: communication and processing activities are not driven by a single global clock Open Distributed Processing

Characteristics of Open Distributed Sytems (ODS)
Heterogeneity: components built using different technologies and the set of various technologies will certainly change over time Autonomy: several autonomous management or control authorities without any single control Evolution: during its working life, many changes (caused by technical progress, strategic decisions about new goals, new types of applications) Mobility: the sources of information, processing nodes, and services may be logically mobile Open Distributed Processing

Problems relating Open Distributed Systems
ODS are important because there is a need to interconnect information processing systems The organizational trends demands the exchange of information both inside the organization and between co-operating organizations The distribution of information processing services is realized in an environment of heterogeneous resources and multiple organizational domains Open Distributed Processing

Integration among services and resources
Open Distributed Processing

A possible solution Capture the representation form of data, the transport protocol for that data, the location algorithm of a service provider etc. Common services: by grouping together the properties of different services and gaining an agreement on these, the amount of heterogeneity in a distributed systems can be structured in a controllable way A framework for system specification is needed that supports such a structuring of the features of distributed systems into common services: this is provided by ODP standardization Open Distributed Processing

What is ODP? Is a standardization activity by ISO providing an object oriented reference model for open distributed system Its objective is to enable the construction of distributed systems in a multi-vendor environment through the provision of a general architectural framework that such systems must conform to Describes systems that support heterogeneous distributing processing both within and between organizations through the use of a common interaction model (Reference Model of ODP ) An architectural framework describes a method for designing an information system in terms of a set of building blocks, and for showing how the building blocks fit together. It should provide a common vocabulary Open Distributed Processing

Properties of ODP systems
ODP standardization enables the building of distributed systems with the following properties: Openess Integration Flexibility Modularity Federation Manageability Provision of quality of service Security Transparency portability : i.e., the ability to execute different components on different processing nodes without modification interworking : i.e., the ability to support meaningful interactions between components, possibly residing in different systems Open Distributed Processing

ODP standardization enables the building of distributed systems with the following properties: Openess Integration Flexibility Modularity Federation Manageability Provision of quality of service Security Transparency Incorporating various systems and resources into a whole without costly ad-hoc developments It covers, for example, integration of systems with different architectures, different resources of different performance. Helps to deal with heterogeneity. Open Distributed Processing

ODP standardization enables the building of distributed systems with the following properties: Openess Integration Flexibility Modularity Federation Manageability Provision of quality of service Security Transparency Supporting a system’s evolution, including the existence and continued operation of legacy systems An open distributed system should be capable of being dynamically reconfigured to accommodate changing circumstances. Helps to deal with mobility. Open Distributed Processing

ODP standardization enables the building of distributed systems with the following properties: Openess Integration Flexibility Modularity Federation Manageability Provision of quality of service Security Transparency Parts of a system are autonomous, but interrelated It is the basis for flexibility Open Distributed Processing

ODP standardization enables the building of distributed systems with the following properties: Openess Integration Flexibility Modularity Federation Manageability Provision of quality of service Security Transparency Combining systems from different administrative or technical domains to achieve a single objective Open Distributed Processing

ODP standardization enables the building of distributed systems with the following properties: Openess Integration Flexibility Modularity Federation Manageability Provision of quality of service Security Transparency monitoring, controlling and managing system’s resources in order to support configuration, QoS and accounting policies. Open Distributed Processing

ODP standardization enables the building of distributed systems with the following properties: Openess Integration Flexibility Modularity Federation Manageability Provision of quality of service Security Transparency Meeting a set of quality requirements on the system’s behaviour Open Distributed Processing

ODP standardization enables the building of distributed systems with the following properties: Openess Integration Flexibility Modularity Federation Manageability Provision of quality of service Security Transparency Ensuring that system facilities and data are protected against unauthorised access. The security requirements are made more difficult to meet by the remoteness of interactions and the potential mobility of parts of the system and of the system users. Open Distributed Processing

ODP standardization enables the building of distributed systems with the following properties: Openess Integration Flexibility Modularity Federation Manageability Provision of quality of service Security Transparency Masking from applications the details and the differences in mechanisms used to overcome problems caused by distribution. This is a central requirement that arises from the need to facilitate the construction of distributed applications. Open Distributed Processing

Realization of ODP There cannot be an single, common infrastructure that provides all of the properties that distributed systems require There is also a need for a framework describing infrastructure components and showing how they fit together The development of a framework for system specification and the corresponding infrastructure components is the general goal of the ODP standardization Open Distributed Processing

Principals Concepts of the ODP
Implement Transparencies: determine how the end users see the system, or more precisely, what they don’t see of the system Viewpoints: a division of system specification in order to simplify the description of complex systems Functions: mask the complexity of a distributed system both user and programmers and connect processes and services Use Open Distributed Processing

Transparencies – general concepts
The programmers and end users should not need to be concerned with the nature and means of distribution Programming and use of a distributed application appears exactly the same as if the application were not distributed at all Uniform view of a system for the end users It’s ODP’s abstraction mechanism Presents a view of what is happening, but hides the how it is happening Open Distributed Processing

ODP Transparencies Are implemented by ODP functions The ODP transparencies are: access transparency failure transparency location transparency migration transparency persistence transparency relocation transparency replication transparency transaction transparency Masks the differences between two or more communicating objects The differences could be in the data representation or in the invocation mechanism between the objects. Is provided by an ODP engineering channel Open Distributed Processing

ODP Transparencies Are implemented by ODP functions The ODP transparencies are: access transparency failure transparency location transparency migration transparency persistence transparency relocation transparency replication transparency transaction transparency Enables fault tolerance in an object or shields an object from failures in the objects environment. Can be implemented by several functions. One such function is the replication function wich replicates an object Open Distributed Processing

ODP Transparencies Are implemented by ODP functions The ODP transparencies are: access transparency failure transparency location transparency migration transparency persistence transparency relocation transparency replication transparency transaction transparency Masks the location of an object in space. Depends on chosing a location independent naming scheme. Enables the named entities to be moved, without notifying all parties who carry a reference to the entity of the changed reference Open Distributed Processing

ODP Transparencies Are implemented by ODP functions The ODP transparencies are: access transparency failure transparency location transparency migration transparency persistence transparency relocation transparency replication transparency transaction transparency Masks changes of location of an object Depends on the migration function Before migration, an object will be checkpointed, and deleted from its original location Once the object is moved, other objects depend on the relocation transparency to find the object again Open Distributed Processing

ODP Transparencies Are implemented by ODP functions The ODP transparencies are: access transparency failure transparency location transparency migration transparency persistence transparency relocation transparency replication transparency transaction transparency Mask from an object the deactivation an reactivation of objects including itself An object does not need to be concerned with loading an object from persistent store before using it Depends on the deactivation and reactivation function Open Distributed Processing

ODP Transparencies Are implemented by ODP functions The ODP transparencies are: access transparency failure transparency location transparency migration transparency persistence transparency relocation transparency replication transparency transaction transparency Masks the relocation of an object from other objects that are referring to it If objects are connected via a channel, and one object is relocated, the channel is reconfigured to the new location of the object Is provided by the relocation function Open Distributed Processing

ODP Transparencies Are implemented by ODP functions The ODP transparencies are: access transparency failure transparency location transparency migration transparency persistence transparency relocation transparency replication transparency transaction transparency Replicates objects in different locations to provide fault tolerance and enhanced performance by better access of data Is provided by the replication function Open Distributed Processing

ODP Transparencies Are implemented by ODP functions The ODP transparencies are: access transparency failure transparency location transparency migration transparency persistence transparency relocation transparency replication transparency transaction transparency masks the coordination between a set of objects required to achieve consistency properties of the objects Is provided by the transaction function Open Distributed Processing

ODP Viewpoints Provide a framework for specifying ODP systems They are not of concern to end users (viewpoint have nothing to do with the end users view of a system: transparencies provide this) Are not independent, but partial view of the complete system specification Distributed system are viewed to be so complex that a process of separation of concerns must be employed when describing such system (“Divide and conquer”) Multiple viewpoint enables different partecipants each to observe a system from a suitable prospective and a suitable level of abstraction Open Distributed Processing

Viewpoints Languages Are associated with a viewpoint They may utilises a different notation, that is best suited for describing a particular area They consist of: a set of definitions a set of rules, wich constrain the ways in wich the definition can be related Open Distributed Processing

Development by viewpoints
Embraces all techniques that involve adding more detail to the specification For example, by including more requirements or by resolving implementation choices Open Distributed Processing

A specification in one viewpoint may need to be translated into a specification in another viewpoint. This is because each viewpoint may utilises a different notation or language, that is best suited for describing a particular area Open Distributed Processing

Is a relation between specification at the same level of abstraction. Two specifications are equivalent in case they capture precisely same requirements Open Distributed Processing

A collection of viewpoint specifications may be integrated into one specification Each viewpoint presents a partial description of the implementation The ultimate aim is to develop an implementation that satisfies all viewpoints Open Distributed Processing

Is a relation between any number of specifications, not necessarily at the same level of abstraction Specifications are consistent with each other, whenever it is possible to find at least one implementation that satisfies them simultaneously Open Distributed Processing

The RM-ODP framework Open Distributed Processing

ODP Viewpoints enterprise viewpoint concerned with the business activities of the specified system information viewpoint concerned with the information that needs to be stored and processed in the system computational viewpoint concerned with the description of the system as a set of objects that interact at interfaces – enabling system distribution engineering viewpoint concerned with the mechanism supporting system distribution technology viewpoint concerned with the components from which the distributed system is constructed Open Distributed Processing

Enterprise viewpoint Is used to organisational requirements and structure. Social and organizational policies can be defined in terms of: Objects “active” objects, e.g. bank managers, tellers, customers “passive”objects, e.g. bank accounts, money communities groupings of objects e.g. a bank branch consists of a bank manager, some tellers, and some bank accounts; the branch provides banking services to a geographical area Roles of the objects within communities, expressed in terms of policies: permission — what can be done, e.g. money can be deposited into an open account prohibition — what must not be done, e.g. customers must not withdraw more than $500 per day obligations — what must be done, e.g. the bank manager must advise customers whenthe interest rate changes Open Distributed Processing

Enterprise Language Is specifically concerned with performative actions that change policy, such as creating an obligation or revoking permission E.g.: In a bank, the changing of interest rates is a performative action as it creates obligations on the bank manager to inform the customers However, obtaining an account balance is not a performative action as obligations, permissions, and prohibitions are not affected Thus, an enterprise specification of a bank need not include the obtaining of account balances; such functionality will be identified in the computational specification Open Distributed Processing

Information viewpoint
Defines the semantics of information and semantics of processing on information in the system This is done using three schema: invariant schema: defines conditions that must always be true on a set of information (state of an object) static schema: that defines conditions that will hold after certain events have occurred dynamic schema: defines transformations (state changes) that can occur on the state of an object in the course of the normal processing, in contrast to a static schema, wich forces an object into certain schema Open Distributed Processing

Information viewpoint - Example
Static schema: at midnight, the amount-withdrawn-today is $0 Invariant schema: the amount-withdrawn-today is less than or equal to $500 Dynamic schema: a withdrawal of $X from an account decreases the balance by $X and increases the amount-withdrawn-today by $X A dynamic schema is always constrained by the invariant schemas Thus, $400 could be withdrawn in the morning but an additional $200 could not be withdrawn in the afternoon as the amount-withdrawn-today cannot exceed $500 Open Distributed Processing

Computational viewpoint
Is used to specify the functionality of an ODP application in a distribution-transparent manner Is object-based, that is: objects encapsulate data and processing (i.e. behaviour) objects offer interfaces for interaction with other objects objects can offer multiple interfaces Defines the objects within an ODP system, the activities within those objects, and the interactions that occur among objects Most objects describe application functionality, and these objects are linked by bindings through which interactions occur Binding objects are used to describe complex interaction between objects (Computational interaction) Open Distributed Processing

Computational viewpoint - Example
Action Interface provided by Bank Branch Object Application objects Open Distributed Processing

Computational Viewpoint Interface Subtyping - Example
The concept of interface type is particularly important in RM-ODP. Interfaces in the computational model are strongly typed and inheritance of an interface type (usually) creates a subtype relationship. Subtypes of an interface type are substitutable for the parent type (or any supertype). Open Distributed Processing

Computational Interaction - Example
BankTeller = Interface Type { operation Deposit (c: Customer, a: Account, d: Dollars) returns OK (new_balance: Dollars) returns Error (reason: Text); operation Withdraw(c: Customer, a: Account, d: Dollars) returns NotToday(today:Dollars,daily_limit: Dollars) } The notation used in the example above is merely illustrative. RM-ODP does not prescribe any particular notation for defining operational interface types Open Distributed Processing

Engineering viewpoint
Is used to describe the design of distribution-oriented aspects of an ODP system Defines a model for distributed system infrastructure Its language defines a number of functional building blocks wich can be combined together to provide the requested transparencies The fundamental entities described in the engineering viewpoint are objects and channels Open Distributed Processing

Engineering viewpoint Objects and Channel
Objects in the engineering viewpoint can be divided into two categories: Basic engineering objects, corresponding to objects in the computational specification Infrastructure objects, e.g. a protocol object A Channel corresponds to a binding or binding object in the computational specification Open Distributed Processing

Engineering viewpoint Example of channel
Supporting Object Supporting Object Supporting Object A channel provides the communication mechanism and contains or controls the transparency functions required by the basic engineering objects Open Distributed Processing

Technology viewpoint Is concerned with the hardware and software components form wich the distributed system is constructed Its language is primarily concerned with referencing appropriate standards and techonologies to use in order to realize the specifications of the other viewpoints Open Distributed Processing

ODP Functions Provide some building blocks to assemble ODP systems They are a collection of functions expected to be required in ODP systems to support the needs of the computational language (e.g. trading function) and engineering language (e.g. the relocator) There is not a simple mapping between transparencies and functions For example, the relocation transparency is exactly what tje relocation function provides, but some transparencies are more implicit in an ODP system, and do not require the support of a function Similarly, many functions provide functionality that is not necessarily a transparency Open Distributed Processing

ODP functions The ODP functions are categorised into four groups: management functions coordination functions repository functions security functions Open Distributed Processing

ODP functions The ODP functions are categorised into four groups: management functions Node management function Capsule management function Cluster management function Object management function coordination functions repository functions security functions Open Distributed Processing

ODP functions The ODP functions are categorised into four groups: management functions coordination functions Event notification function Checkpoint and recovery function Deactivation and reactivatin function Group function Replication function Migration function Engineering interface reference tracking function Transaction function ACID transaction function repository functions security functions Open Distributed Processing

ODP functions The ODP functions are categorised into four groups: management functions coordination functions repository functions Storage function Information organization function Relocation function Type repository function Trading function security functions Open Distributed Processing

ODP functions The ODP functions are categorised into four groups: management functions coordination functions repository functions security functions Acces control function Security audit function Authentication function Integrity function Confidentiality Non-repudation function Key management function Open Distributed Processing

Software development process in ODP
The development process is decomposed according to viewpoints Each viewpoint deals with a particoular area of concern and, therefore, focuses on those aspects of the system under development that are relevant to that area of concern Open Distributed Processing

Consistency between viewpoints
The five viewpoints specifications must be linked by defining the relations between key terms in them. It is these statements of the relationships between veiwpoints that make them specifiy a single system, rather than being completely independent documents Many of the links will be provided implicity by the notations used, resulting from correspondence between names. However, some of the key constraints need to be stated explicitly Constraints are placed on the relations between terms in the viewpoint language themselves, establishing some limits on the mappings which can be established Most of the constraints placed are between terms in the computational and engineering languages Open Distributed Processing

Example of consistency between viewpoints
If such correspondence cannot be established, then the two different description are not consistent, and should be refined untile a correspondence can be demonstrated Open Distributed Processing

Enterprise viewpoint consistency vs. other viewpoints
The enterprise language should serve as the basis for specifying enterprise goals which must be reflected directly or indirectly in all other viewpoint specifications. The enterprise viewpoint describes, explicitly, the objectives of the system in the context of the organization in terms of members, roles, actions, purposes, usage and policies. Therefore, an information, computational, engineering or technology viewpoint specification is consistent with an enterprise specification if all the roles, activities, and policies described in the enterprise specification are correctly reflected. For instance, dynamic schema defined in an information specification must obey the policies described in the enterprise specification. Different roles identified in the enterprise specification may be supported by different computational objects, having different transparency requirements. Thus, transparency needs for each role in the enterprise specification should be reflected by the use of the corresponding transparency mechanism in the engineering specification Open Distributed Processing

Correspondence between computational and engineering viewpoints

Other concerns in ODP System
Formal Descriptions Consistency between viewpoints described with different notations Conformance assessments Other ODP projects: INTAP, which uses UML Profile for EDOC (Enterprise Distributed Object Computing) from OMG and RM-ODP viewpoints ATA, architecture which respect ODP standards Open Distributed Processing

INTAP: example of enterprise viewpoint

Special icon is used to represent role of the community in the diagram Open Distributed Processing

The behavioral part of the community could be specified with UML Collaboration. Open Distributed Processing

INTAP: example of information viewpoint
Instance model description Open Distributed Processing

Structured class diagrams for instance model Open Distributed Processing

Dinamic schema Open Distributed Processing

References ODP Reference Model ftp://ftp.dstc.edu.au/DSTC/arch/RM-ODP/PDFdocs/ Reference Model of Open Distributed Processing (RM-ODP): Introduction Kerry Raymond - ODP: Unplugged! Ian Joyner RM-ODP: The ISO Reference Model for Open Distributed Processing Antonio Vallecillo - ETSI Informática. Universidad de Málaga FDTs for ODP Howard Bowman, John Derryck, Peter Linington and Maarten Steen Computing Laboratory, University of Kent, Canterbury Applying EDOC and MDA to the RM-ODP Engineering and Technology Viewpoints An Architectural Perspective David Frankel Consulting Open Distributed Processing

Open Distributed Processing

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